The inter-relationship between the internal environment of buildings and the external environment is likely to alter in the presence of climate change. The potential implications of this changing relationship for the health and comfort of housing occupants in Neath Port Talbot (NPT), south Wales, are considered in this thesis through an analysis of health and comfort risk systems. A literature review of climate change, occupant thermal comfort, health and housing and architecture has been undertaken to establish the risk systems for risks to occupant health and comfort through the application of the source-pathway-receptor model of risk. This review has been summansed through the production of risk matrices including an evaluation of the potential for increase or decrease in the risk to occupant heath and comfort in the domestic environment due to climate change. Questionnaire surveys were undertaken to establish the current distribution of occupant hearth and comfort risks in households in NPT dunng hot summers and average winters, considered as temporal proxy for future average conditions. Further to this these surveys considered the influence of occupant behaviour and housing, neighbourhood and socio-economic factors. Detailed monitoring of a case study home, built in the year 2000, was also undertaken, using temperature and relative humidity loggers. An air leakage test and thermography survey were also undertaken. This enabled a quantitative analysis of conditions in relation to comfort thresholds dunng the hot summer of 2003. It has been found that homes in NPT present health and comfort risks to their occupants under current extreme climate during both the winter and summer. These risks include inadequate and excess heating, damp and mould and inadequate ventilation levels. Future work should focus on quantitative impact research and risk distribution in housing, as well as on passive methods to alleviate summer overheating, in order to avoid an increase in energy usage for cooling and its potential impact on climate change mitigation.